1. Field of Invention
The present invention relates to a motor control apparatus, which can synchronize the phases of a phase switching signal and a current phase signal so as to promote operation efficiency of the motor.
2. Related Art
Conventional motor operation is enabled through interaction between a stator and a rotor, which are two major components in the motor, oppositely disposed in a motor. By providing magnetic attraction and magnetic field variation, the motor can induce a rotation of the rotor corresponding to the stator. In the motor operation, the magnetic field variation represents commutation of the magnetic pole of the motor. As shown in FIG. 1, a current motor 2 generally uses an electronic phase converter for commutation. In more detailed, the electronic phase converter regularly uses a Hall sensor 13 to detect the position (or the magnetic field variation) of the magnetic pole of the motor 2 for determining the rotor position. The driving integrated circuit 11 then outputs a driving signal Sd to a driving circuit 12 in order to control the coil currents in the stator of the motor 2 to switch mutually for commutation in accordance with the phase switching signal Sp generated by the Hall sensor 13.
Moreover, the detecting ability of the Hall sensor 13 for the magnetic field variation depends on the rotating speed of the motor 2 and the disposed position of the Hall sensor 13. Therefore, the Hall sensor 13 must be arranged on the most feasible position for accurate detection. As shown in FIG. 2, the Hall sensor 13 in the conventional direct-current (DC) brushless motors is always purposely disposed forwardly (between the slot openings of the silicon steel plates of the motor 2, and closer to one of the silicon steel plates) for leading commutation in order to promote the motor efficiency at rating rotating speed and form current waveform Si as shown in FIG. 3 (the current with higher efficiency presents an evener waveform).
However, the Hall sensor 13 cannot automatically shift to a feasible position after the rotating speed of the motors 2 is changed. Once the rotating speed of the motor 2 is controlled at a slow speed, the motor 2 efficiency declines from the optimal status and the current waveform is not as even as the original. As shown in FIGS. 3B and 3C, when the loading is changed (when the fan is in back pressure) or the voltage source is changed, it probably results in a leading or lagging magnetic phase of the phase switching signal Sp detected by the Hall sensor 13, which causes the motor 2 efficiency falls from the optimal point as well. Meanwhile, the current of the motor 2 is either leading (with a protruding front portion) or lagging (a protruding back portion) can be indicated from the current waveform Si of the motor 2. Because of it, the driving IC may output an improper driving signal Sd to the driving circuit 12 so as to cause an unsmooth commutation of the motor 2 and induce noise. Particularly, when the motor 2 is used for fan application, the heat dissipation efficiency of the fan is consequently decreased.